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Why some animal species have disappeared?
Throughout the pass of the years a lot of animal species have disappear without leaving a trace to respond the one million question “why some animal species have disappear while others still exist”. Thousands of paleontologist and even archeologists have made numerous researches looking for an answer to this natural or unpredictable phenomenon. The percentage of animals in extinction are alarming, according with most researches 99% of all the species ever on the earth are now extinct. Several times during the history of the earth there have been critical periods in which the rates of extinction increase until the point of the total extinction of many species like in the case of the dinosaurs. Nowadays, there are two main and strong explanations that attempt to clarify the reasons why extinction occurs. One of those hypotheses involves catastrophic changes and the other is concerned on gradual changes such as the climatic changes.
The hypothesis based on the catastrophic changes support the idea that the impact of asteroids and the intense volcanic activity could be the cause of mass extinction. According to this theory, the two events mentioned before destroyed a huge part of the natural recourses where animal used to feed by themselves. The amount of dust that is left into the air result in the reduction of photosynthetic production, and when this happen a lot of plants died that means the food of many animal species. A clear example of this phenomenon was the Cretaceous/Tertiary extinction which occurred thousand of millions years ago. It is known that in this mass extinction was found the element “iridium” in rock strata, and this came to support the catastrophic hypothesis. Iridium is a primarily extraterrestrial element that is deposited during asteroid impact with the earth and also this element may result from volcanic activity. However, there is a contradiction in this hypothesis, it is supposed that catastrophic events must affect at least most of animal groups which was no the case with the Cretaceous/Tertiary extinction because just dinosaurs became extinct but crocodiles, bird and other species did not.
On the other hand, many researchers believe that mass extinction is the result of gradual or selective changes. According to this hypothesis climatic changes are related with mass extinction, and these changes could start with the continental drift. Taking the Cretaceous period as an example, we can see how climatic changes affect the life on the earth. In this period 70% of the present land area was covered by warm, shallow seas. By the end of the Cretaceous period, these seas were reduced to 15% of the present land areas. That means that there was a reduction of the habitat for shallow-water marine organism. Those climatic and habitat changes could have resulted in the extinction over periods of tents of thousands of years.
Even though both hypotheses have some supported evidence, none of them have been accepted as true completely. So each side has looked for more evidence that can prove their hypothesis. Nowadays, the gradualism/catasthophism has led to new, innovative ideas on the origin, evolution and extinction taxa.
Throughout the pass of the years a lot of animal species have disappear without leaving a trace to respond the one million question “why some animal species have disappear while others still exist”. Thousands of paleontologist and even archeologists have made numerous researches looking for an answer to this natural or unpredictable phenomenon. The percentage of animals in extinction are alarming, according with most researches 99% of all the species ever on the earth are now extinct. Several times during the history of the earth there have been critical periods in which the rates of extinction increase until the point of the total extinction of many species like in the case of the dinosaurs. Nowadays, there are two main and strong explanations that attempt to clarify the reasons why extinction occurs. One of those hypotheses involves catastrophic changes and the other is concerned on gradual changes such as the climatic changes.
The hypothesis based on the catastrophic changes support the idea that the impact of asteroids and the intense volcanic activity could be the cause of mass extinction. According to this theory, the two events mentioned before destroyed a huge part of the natural recourses where animal used to feed by themselves. The amount of dust that is left into the air result in the reduction of photosynthetic production, and when this happen a lot of plants died that means the food of many animal species. A clear example of this phenomenon was the Cretaceous/Tertiary extinction which occurred thousand of millions years ago. It is known that in this mass extinction was found the element “iridium” in rock strata, and this came to support the catastrophic hypothesis. Iridium is a primarily extraterrestrial element that is deposited during asteroid impact with the earth and also this element may result from volcanic activity. However, there is a contradiction in this hypothesis, it is supposed that catastrophic events must affect at least most of animal groups which was no the case with the Cretaceous/Tertiary extinction because just dinosaurs became extinct but crocodiles, bird and other species did not.
On the other hand, many researchers believe that mass extinction is the result of gradual or selective changes. According to this hypothesis climatic changes are related with mass extinction, and these changes could start with the continental drift. Taking the Cretaceous period as an example, we can see how climatic changes affect the life on the earth. In this period 70% of the present land area was covered by warm, shallow seas. By the end of the Cretaceous period, these seas were reduced to 15% of the present land areas. That means that there was a reduction of the habitat for shallow-water marine organism. Those climatic and habitat changes could have resulted in the extinction over periods of tents of thousands of years.
Even though both hypotheses have some supported evidence, none of them have been accepted as true completely. So each side has looked for more evidence that can prove their hypothesis. Nowadays, the gradualism/catasthophism has led to new, innovative ideas on the origin, evolution and extinction taxa.
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